Use of carbonaceous fuels

ABSTRACT

A process for the gasification of carbonaceous fuels, for, inter alia, the production of chemicals and/or the generation of power is described, characterised in that there is employed, as starting material or part thereof, coal in the form of an aqueous slurry, the aqueous (water) content of the said slurry being at least 55 to 80% by weight. There is also described an apparatus for the burning of carbonaceous fuel, for the production of electrical energy, which apparatus comprises, in interconnected combination, a gasifier into which aqueous coal slurry is introduced, a flow drier/separator wherein materials exiting the gasifier are dried and separated into gaseous component and dried slurry material with feeding of the latter back to the gasifier, a cooling/cleaning device into which the gaseous component from the separator passes and from which, when cleaned, it proceeds for further processing, a gas turbine generation unit in turn comprised of compressor, expansion stage, and generator, and a combustor mechanism; the arrangement being such that combustion and process air passes from the turbine compressor in one stream to the gasifier and in another stream to the combustor, where the latter is combined with the gaseous component from the cooling/cleaning device, the combined gasses then being passed to the expansion stage of the gas turbine generation unit, and converted therein into electrical energy.

FIELD OF THE INVENTION

The problems associated with the use of coals as a gas turbine fuel forhigh efficiency power generation are well known. This invention isdirected to the provision of an improved process and apparatus wherebysuch problems are overcome or, at the least, considerably alleviated.

BACKGROUND

(i) Current conventional wisdom is that direct firing of coal or the useof hot, substantially uncooled gas from a coal gasifier is probably thebest means to achieve high generation efficiencies with coal-fired gasturbine systems. However, it is known that ash particles, vaporisedsalts, and sulphur compounds which result from direct coal firing orfrom the use of hot gases from coal gasifiers, are difficult toeliminate without substantial cooling of the gases.

(ii) It is known that cooling and washing of gas leaving coal gasifierscan substantially remove all the compounds which give rise to problemswith high temperature components in gas turbines. However it is acceptedthat such a cooling and washing produces a very dilute fuel gas heavilycontaminated with water vapour which is generally regarded as beingunsuitable for combustion in conventional gasifiers. In some currentlyproposed schemes for Integrated Gasification Combined Cycle processes(known in the art as IGCC processes), fuel gas produced by simple totalor partial adiabatic cooling of gasifier product gas also lowers theflame temperature of the diluted fuel gas to the point where stablecombustion and the high combustion temperatures required by highefficiency IGCC system designs are not attainable with the highly watervapour-diluted coal-based fuel gases.

(iii) It is generally accepted that, notwithstanding the known problemsof added complexity caused by the introduction of additional equipment,efficient coal firing of gas turbines can only be achieved with the useof combined cycles, ie. the incorporation of a waste heat boiler in theturbine exhaust and the use of a steam turbine cycle.

(iv) It is also conventional wisdom to consider that higher compressionratio turbines are the optimum means to achieve high efficiency withcoal-fired gas turbine systems even though such turbines present knownproblems associated with the use of high compression ratios. Theproblems of drying and gasification of carbonaceous fuels andparticularly high water content carbonaceous fuels such as lignite, whenused as a power generation fuel or feedstock for synthesis gasproduction, are also well known.

(v) Prior Art Proposal

The foregoing problems are outlined in a recent prior art developmentwhich proposes a means and process whereby solid moisture-containingcoal can be utilised to generate power. According to this proposal, theprocess cannot however readily deal with a solid lignite having asignificant moisture content if it is converted into a water-ligniteslurry typically containing 25% or possibly less solids (wet basis).Even though the higher water content lignite could be more readilyhandled, it was apparently considered that loss of efficiency of theoverall process and also the known problems in combusting water vapourladen, very low heating value fuel gas in gas turbines would be toodisadvantageous. Consequently, the use of such a coal slurry wasapparently considered to be not technically feasible and to be likely toresult in major combustion problems, and inability to achieve a highcombustion temperature with consequent low power generation efficiency.

In this (solid fuel) proposal, the fuel gas leaving the drier integratedwith the gasification process is to be further adiabatically cooled bythe injection of water and the saturated gas is then washed or treatedby known means to remove particulates, and is then further cooled toreduce the water content of the gas such that it is increased incalorific value and can be used in known combustion systems. Gastreatment at water saturation temperature can remove particulates andmay also enable the removal of sulphur compounds by known meansfollowing that stage. This final cooling has the inherent disadvantageof removing water vapour at combustion pressure which could be heated inthe combustion stage and a significant part of its inherent energyrecovered in the expansion stage of the turbine. By condensing the watervapour this inherent energy is wasted and the cooling stage requiresextra equipment and cooling media to remove the water vapour and aprocess plant to handle the resultant condensate.

The cooling of the gasifier exit gas by simultaneous drying of the coalfeed puts additional water vapour into the fuel gas, and furtheradiabatic cooling by water addition and water washing for removal ofsolid particles and possibly sulphur compounds after the drying stageputs water vapour at combustion stage pressure (which could increase themass flow to the combustion and final expansion stage thereby increasingthe rated power output of the turbine system). However the additionalwater content added by such cooling has the problem of making the gasunsuitable for combustion and for the achievement of high combustiontemperatures such as in excess of 1,100° C. and preferably above 1,200°C.

It is also known, and referred to in this prior art, that it has beenproposed that wastes such as sewerage sludge can be dried by contactingsaid wastes with the hot gases leaving a coal gasifier. However such asystem also suffers from the limitation that the amount of water whichcan be evaporated is limited by known gas turbine and turbine combustionsystems. These limitations also constrain the use of simple water sprayand gasifier exit gas cooling and ash removal systems.

The problems of NOX (oxides of nitrogen) formation in fossil fuel firedgas turbines are well known. The prior art proposal envisages the use ofconventional known combustion systems which, even with best practicecombustor design, would result in a NOX content in the exhaust gas of inexcess of 10 ppm (and probably about or in excess of 20 ppm).

Further Known Problems

(vi) It is known that oxygen should preferably be used for coalgasification where the product gas is to be used to synthesise methanolor methanol derivatives. However for such gasification processes, thereduced flow of produced gas compared to coal feed rate makes integrateddrying and gasification difficult. It has been believed that, due tolack of sufficient hot gas needed to dry the coal prior to gasification,the use of oxygen-blown gasifier gas to dry a significantly wet lignitefeed cannot be achieved.

(vii) It is also known that gasification processes developed forbituminous coal--such as the processes commercially known as U-Gas andShell Totzec which operate at pressure, require a dry coal feed andtherefore cannot use a pumped water/coal slurry--require the use of lockhopper systems to pressurise the coal prior to being fed to thegasifier. The gas mixture in the gasifier is flammable and toxic andsuch feed systems require special equipment to recover and use thesegases.

(viii) A further known problem with IGCC cycles, particularly air blowngasifier processes, is that, to enable conventional burner systems tooperate satisfactorily, it is necessary to operate the gasifier at asignificantly higher pressure than the pressure to which the combustionair is compressed.

SUMMARY OF THE INVENTION

Against the cumulative background of the foregoing, the invention ofthis application is predicated upon our finding that, surprisingly,against all expectations, coal material with a substantial aqueous(water) content can be utilised as the basic starting material in thegasification of coal fuel and the generation of power. Accordingly, theinvention, in its broadest aspect, provides a process for thegasification of carbonaceous fuels, for, inter alia, the production ofchemicals and/or the generation of power characterised in that there isemployed, as starting material or part thereof, coal in the form of anaqueous slurry, the aqueous (water) content of the said slurry being atleast 55% by weight.

In a related aspect, the invention further provides a process a processfor the gasification of carbonaceous fuels, for, inter alia, theproduction of chemicals and/or electrical energy characterised in that

(i) coal, in the form of an aqueous slurry having a water content of atleast 55% by weight, is introduced, with hot gas produced in a coalgasifier stage, to a drying stage,

(ii) the resultant slurry mixture is dried in the said drying stage bythe adiabatic cooling of the hot gas and evaporation of the water, thethus dried coal and the cooled humidified gas being separated withreturn of the dried coal to the hot-gas producing gasifier stage, and

(iii) the cooled humidified gas is further cooled, cleaned and utilisedin the production of chemicals and/or electrical energy.

Preferably, the aqueous content of the slurry is at least 65% by weight,and optimally it is in the range 70-80% by weight. The coal slurry maybe composed in whole or in part of a slurry further comprising coalwashery tailings residue. In a further (effluent eliminating) aspect,the aqueous medium, for the coal slurry, may be comprised, in whole orin part, of waste water, sewerage and the like.

Relatedly the invention also provides apparatus for carrying out theabove-defined process. In one aspect the apparatus comprises, ininterconnected combination, a gasifier into which aqueous coal slurry isintroduced, a flow drier/separator wherein materials exiting thegasifier are dried and separated into gaseous component and dried slurrymaterial with feeding of the latter back to the gasifier, and acooling/cleaning device into which the gaseous component from theseparator passes and from which, when cleaned, it proceeds to arecuperator turbine/combustion arrangement for power generation.

In a further aspect, the invention also provides apparatus, for use incarrying out the above defined process which comprises, ininterconnected combination, a gasifier into which aqueous coal slurry isintroduced, a flow drier/separator wherein materials exiting thegasifier are dried and separated into gaseous component and dried slurrymaterial with feeding of the latter back to the gasifier, acooling/cleaning device into which the gaseous component from theseparator passes and from which, when cleaned, it proceeds for furtherprocessing, a gas turbine generation unit in turn comprised of acompressor, expansion stage, and generator, and, a combustor mechanism,the arrangement being such that combustion and process air passes fromthe turbine compressor in one stream to the gasifier and in anotherstream to the combustor, where the latter is combined with the gaseouscomponent from the cooling/cleaning device, the combined gasses thenbeing passed to the expansion stage of the gas turbine generation unit,and converted therein into electrical energy.

In further preferred aspects of the invention (elaborated in detaileddescription below)

The lignite/brown coal/high water content semi bituminous coal being fedto the drying stage of the process is fed by pumping, or other knownmeans, as a slurry or paste of size reduced, but otherwise untreated "asmined" lignite or coal. This feed material has a water content in therange 70-80% by weight of water.

Combustor system for the turbine comprises two combustion stages, thefirst stage being a combustor in which sufficient fuel gas is intimatelymixed with the combustion air prior to the first stage of combustion togive a temperature in excess of 800° C. and below 1,000° C. at whichtemperature the mixture leaves the first stage. The remaining part ofthe fuel (as required) is added under conditions which ensure maximummixing and turbulence such that free radical induced rather than flameinduced combustion is favoured. An example of such a combustor isdescribed in the specification of application PCT/AU95/00719 which isincorporated herein by reference.

The fuel gas passing to the second stage of combustion is catalyticallyreacted (e.g. per medium of known sulphur tolerant shift catalysts) toconvert at least part of the carbon monoxide and water vapour in the gasstream to hydrogen and carbon dioxide before passing to the said secondcombustion stage. This further increases its temperature and hydrogencontent to ease its combustion in lean phase mix with combustion gasesby means of free radicle-induced combustion.

The gases leaving the coal gasification stage, or at least the greaterpart thereof, are used to dry the coal (lignite) water slurry and thegases are then further cooled by evaporative cooling by further wateraddition, water washing being thereby used to remove solid particlesfrom the gas (by known means such as venturi scrubbers, water sprays,coalescers, demisters, electrostatic precipitators). Thereafter thegases can be preheated by heat exchange with exhaust gases leaving theexpansion stage of the gas turbine before being used as fuel gas in theturbine's combustion system.

Salts may be removed by solution in the wash water and fuel and ashcomponents may be separated by known means. Unused fuel may be recoveredas a water/fuel slurry and recycled with the incoming fuel/water slurryfeed.

The water content in the coal may be due in whole or in part to theaddition of wastes such as sewerage waste or other suitable wastesrequiring disposal which may be added together with the coal or lignitefuel.

The process of this invention is also suitable for the use oflignite/water slurries where the lignite has been pre-treated by theHydro Thermal Dewatering process (known as the HTD process). With theuse of the denser slurry produced by the HTD process, an integrateddrying and gasification process producing power in accordance with thisinvention can dry a feed coal and water slurry in excess of thatrequired for power generation and can produce a side-stream of driedcoal for oxygen-based gasifiers producing synthesis gas for coalprocessing plant such as hydrogenation to produce liquid fuels or otheruses such as a low moisture high quality briquette fuel.

By means of using the combustor system specified in this invention thepressure of the air passing to the gasifier may be no more than 4.0 barand possibly less than 2 bar above the pressure of the air passing tothe combustor.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic representation of a preferred embodiment of aprocess for the gasification of carbonaceous fuels.

DETAILED DESCRIPTION OF THE INVENTION

Attention is now directed to the accompanying drawing wherein FIG. 1depicts, schematically, a preferred embodiment of the invention. In thefigure, the apparatus of the invention, which is used in the performanceof the process of the invention is illustrated.

In the preferred embodiment, the aqueous coal slurry is an aqueousslurry of lignite, lignite being a well-known brown coal with a carboncontent within the range 25-45%. In its detail (namely particle size,water content et al) the lignite slurry is discussed further below. Itis re-emphasised that the figure is a schematic illustration and is tobe understood as such.

In the drawing item 2 is an air blown pressurised lignite gasifier (suchas a Winkler gasification device) and item 4 is an outlet duct of thegasifier to which additional air or oxygen may be optionally added viapipeline 132. Items 6, 8 and 10 are components of an entrained flowdrier of known construction in which 6 is an entrainment mixing vesselin which fluidisation and conveying of lignite is initiated, 8 is anentrainment flow drying tube or tubes, and 10 is a separator orseparators such as a cyclone separator or separators. Item 12 denotes adried lignite feeding device which may be a screw conveyor, lock hoppermechanism, injector or any combination of such known devices, which caninject dried lignite into the gasifier which is at a higher pressurethan the lignite recovered from separator 10.

Item 14 is an adiabatic cooling device such as a venturi scrubber, whichis capable of cooling hot and dust laden gases to their dew point,coagulating mist particles and wetting dust particles in the gas stream.Item 16 is a separator, such as a cyclone separator and mist eliminationsystem or electrostatic precipitator or the like, which may incorporatewater spraying or partial condensation to provide a clean water washcapable of removing substantially all of the dust particles and solublesalts as a solution or slurry which is separated from the gas streamwithin separator 16 and removed via pipeline 146.

The apparatus also comprises a recuperated turbine and combustion systemwhich will now be described.

Items 18, 20, 22, 24 and 26 depict a gas turbine power generation unitin which 18 is the air compression stage, 22 is the expansion stage, 26is the generator and 20 and 24 are respective connecting shafts between18 and 22 and 22 and 26. The expansion stage, 22 may be a split orsingle shaft unit. Items 28 and 32 are sets of recuperators. In thecombustion system, item 34 is a first stage combustion vessel(combustor), which may be of the type described in the copendingapplication referred to above. Item 36 is an interconnecting duct anditem 38 is a second stage combustion vessel (combustor) in whichcombustion is achieved as described hereafter.

The gas turbine may have a compression ratio less than 35/1, for examplebelow 17/1, and may be as low a 4/1.

Item 40 is a catalytic system incorporating known (e.g. sulphurtolerant) shift catalysts mounted in a vessel such that part of thecarbon monoxide in the gas stream entering the vessel reacts with thewater vapour in the gas stream to form additional hydrogen and carbondioxide.

Air from the gas turbine compressor 18, at a lower pressure than the airin pipeline 124, is withdrawn from the compressor and fed via pipelineor duct 120 into the recuperator sets 28 and 32 and passes via pipelineor duct 122 to the first stage combustor, 34.

Steam is added to the gasifier, 2, by known means via pipeline orpipelines 150 and dried lignite is fed via the feeding device 12. Ashand partially combusted lignite are withdrawn by known means via extractsystem, item 134.

Hot gases typically at between 900° C. and 1,000° C. pass from thegasifier 2 to duct 4. As indicated above, additional air and/or oxygenmay be added to raise the exit gas temperature via pipeline 132.

The hot gases leaving the gasifier in duct 4 enter mixing vessel 6 andslurried lignite is added via pipeline 102. The lignite slurry in thiscase is "as mined" lignite reduced in size to particles of dimensionsless than 10 mm and suspended in water as a dense slurry or paste havinga dry lignite content of about 25% by weight on an "as fed wet" slurrybasis. The drying lignite and mixed hot gases and water vapour enter 10in which the greater part of the dried lignite is removed and pass tofeeding device 12 in which the lignite is conveyed at a controlled rateand increased in pressure such that lignite passes to the gasifier, 2.Part of the steam shown as entering the gasifier may be used to assistin the conveyance and dispersion of the lignite from device 12 togasifier 2.

Any leakage of gas via the feeding device 12 would pass to separator 10and would be recovered as gas turbine fuel.

Gas from the combined gasification and drying stages leave separator 10via pipeline or duct 104 and enters cooling device 14 in which water isadded via pipeline 106 to cool and saturate the gases to or slightlybelow their adiabatic dew point. The excess water plus dissolved andsuspended salts and ash from the lignite plus unburnt or partially burntlignite are removed via pipeline 146. The material leaving via thepipeline may be treated by known means to extract ash and to remove andrecycle the unburnt and partially burnt lignite. All or part of thelignite may be utilised in the production of the aqueous slurryintroduced via pipeline 102. Remaining salts and water may be treated inorthodox fashion.

The cleaned fuel gases, which also contain a substantial amount of watervapour and inert gases such as nitrogen and carbon dioxide, leavecooling device 14 via pipeline 108 and pass to the recuperator 32 inwhich the gas is preheated for passage to and use as fuel in theabove-mentioned gas turbine combustor system (34, 36 and 38, 18, 20, 22,24, 26).

Combustion and process air for the gas turbine system enters the systemvia duct 118 and is compressed in compressor 18 such that compressedcombustion air is withdrawn via pipeline 120 and preheated inrecuperators 28 and 32 and then passes via duct 122 to the first stagecombustor 34.

Some air at a higher pressure than in pipeline 120 is withdrawn viapipeline 124 and passes via this pipeline to the gasifier in which theair is injected into the gasifier via pipelines 128, 130 and(abovementioned) 132.

Air stream 124 may be recuperated prior to passage to the gasifier via arecuperator in parallel with recuperators 28/32 so as to increasegasification temperature. In this embodiment total gasifier temperaturemay be raised, or alternatively, part of the air is pre-heated and usedto partially fuse and agglomerate coal in a fluid bed gasifier.

The combustor 34 is operated so as to use all or the greater part of theair preheated in recuperators 28 and 32 and entering the combustor viapipeline 122, and part of the preheated fuel gas from recuperators 28and 32 entering the combustor via pipeline 110 and 112. The combustionproducts are then transported to combustor 38 via duct 36 at typicallybetween 850° C. and 1,000° C. The remainder of the fuel passes frompipeline 110 to pipeline 114 and enters catalytic system 40 in whichpart of the carbon monoxide in the gas is converted by reaction withwater vapour in the gas by known catalysts into additional hydrogen withan increase in temperature due to the exothermic nature of the reaction.The hydrogen enriched gas then passes via pipeline 116 to the secondstage combustor 38.

The resultant combustion gases leaving combustor 38 are at a temperaturein excess of 1,000° C. and preferably above 1,200° C. before enteringthe expansion stage 22 of the turbine via 136. Net surplus powerproduced in the expansion turbine 22 passes via shaft 24 to generator 26in which it is converted predominantly into electrical energy.

The flow of and use of part of the air flow in the gas turbine forpurging and cooling operations (such as turbine blades, diaphragms,stator nozzles, shafts, casings and the like) is carried out in knownfashion.

In the aforementioned process sulphur in the initial coal feed isremoved in or downstream of the gasifier according to methods well knownin the art.

In practice, and in brief recapitulation of the above, the firstcombustor may be fired with fuel oil (diesel) for start up purposes. Theaqueous lignite slurry is fed into the outlet duct of the gasifier andsteam, air, enriched air or oxygen are fed into the gasifier. As hotgases, typically at a temperature in the range 900 to 1,000° C., leavethe gasifier, then traverse the duct through which the slurried ligniteenters. The mixture of gases, slurried lignite and drying ligniteproceed via the entrained flow dryer sequentially comprised of theentrainment mixing vessel, the flow drying tube and the cycloneseparator. The components enter the separator wherein the greater partof the dried lignite is recovered and passes to the screw conveyor orother feeding device for feeding into the gasifier.

Gas leaving the cyclone separator passes via a pipeline to the adiabaticcooling device (venturi scrubber) to which water is added via a pipelineto cool and saturate the gases to or slightly below their adiabatic dewpoint. Herein, excess water, plus dissolved and suspended salts and ashfrom the lignite, plus any unburnt or partially burnt lignite, areremoved via the exit pipeline. The fuel gases, which have been cleanedby the water from the pipeline entering the venturi scrubber, and whichalso contain water vapour plus nitrogen and carbon dioxide, leave thescrubber via a pipeline and pass to the recuperators. Here the gas ispreheated for use as fuel in the associated gas turbine system which iscomprised of the air compressor, expansion stage, generator andrespective connecting shafts.

Further associated with the gas turbine system and the recuperators area first stage combustion vessel and a second stage combustion vessel.The vessels are interconnected by a duct. In the second stage vessel,combustion is achieved by the rapid and intimate mixing of the remainingfuel gas with the hot gases from the recuperators such thatpredominantly free radical rather than flame initiated combustion takesplace.

Combustion and process air, for the gas turbine system, enters the aircompressor via an entrance duct and compressed air exits via twopipelines. The exiting air in one pipeline, at a lower pressure than theair in the other pipeline, travels to the recuperators and thence to thefirst combustor. The higher pressure air passes to the gasifier via theappropriate pipelines.

In addition to the air entering from the compressor via therecuperators, the first combustion vessel is also fed with portion ofthe abovementioned cleaned preheated fuel gas which has travelled fromthe venturi scrubber. The combined combustion products from the firstcombustion vessel are transported to the second vessel via theconnecting duct at a temperature typically within the range 850 to1,100° C. The remainder of the cleaned fuel gas from the scrubber entersa sulphur tolerant catalytic system wherein there is a reaction betweenthe incipient carbon monoxide and water vapour to form additionalhydrogen and some carbon dioxide. The thus hydrogen-enhanced gas thenpasses, via pipeline, to the second combustor vessel.

This second vessel thus contains air and gas from the first combustionvessel and further fuel gas from the gasifier and flow drier (via thescrubber). The combustion gases leaving the second combustion vessel areat a temperature in excess of 1,100° C. whereupon they enter theexpansion stage of the turbine system. Power produced therein passes tothe generator wherein it is converted into electrical energy.

In the alternative embodiment where all of the cleaned fuel gases passesto the combustor 34, items 38 and 40 need not be utilised. Accordingly,a single combustor may be utilised in this embodiment.

The invention will now be further described with reference to thefollowing Examples 1 and 2.

EXAMPLE 1

In this example, which is carried out with apparatus as schematicallyillustrated immediately above, parameters are as follows:

(i) A wet lignite and water slurry with 75% (wt/wt) water is fed viafeed system 102.

    ______________________________________                                                                     %                                                          Lignite analysis (dry and ash free basis)                                                        (wt/wt)                                          ______________________________________                                                    C                    68.2                                                     H2                   4.4                                                      N2                   0.6                                                      S                    0.3                                                      O2                   26.5                                                     0.7% ash (moisture free basis)                                    Higher heating value                                                                      26.11 MJ/Kg (dry and ash free basis)                              ______________________________________                                    

(ii) The turbine compressor would compress air to 10 atmospheres fromwhich air would be bled for preheating and use in the gasifier and theremaining air would pass through an expansion stage on the same shaftenabling the remaining air to leave at 8 atmospheres for preheating bythe recuperator in the gas turbine exhaust gases and use as combustionair.

(iii) The streams of air exiting the compressor are respectively at 8and 10 atmospheres.

(iv) The temperature of gases entering the combustor and entering theturbine expansion stages are 1,250° C.

(v) Power generation efficiency based on the HHV of the feed lignite(after allowing for recoverable energy in the char and ash residueleaving via extraction systems 134 and 146) is 38%.

(vi) NOX emissions in the flue gases leaving the plant would be lessthan 5 p.p.m.

EXAMPLE 2

In a further example of drying a coal slurry, gasifying the coal andgenerating power using bituminous coal, a slagging gasifier using oxygeninstead of air for the partial oxidation/gasification of the coal isused. In this case air compressed by the turbines air compression stageis withdrawn at the compressor exit with part of the air being used asfeed to the combustor and the remainder being feed an air separationunit. By using the known technique of liquid oxygen pumping the airseparation plant can supply oxygen at a pressure above that of the feedair thus eliminating special air compression normally required for theoptimal operation of coal gasifiers which are integrated with gasturbine systems.

In this example a nominal 25 MW recuperated gas turbine is used havingthe following characteristics:

    ______________________________________                                        Compressor efficiency       95%                                               Turbine efficiency          95%                                               Recuperator effectiveness   90%                                               Cooling air                 13%                                               Turbine inlet temperature   1,070° C.                                  Compression ratio           8 to 1                                            At sea level and at 15° C. the turbine is capable of producing         27.2 MW                                                                       when integrated with coal gasification, coal slurry feed, drying and          fuel                                                                          gas treatment system having the following characteristics.                    ______________________________________                                    

At sea level and at 150° C. the turbine is capable of producing 27.2 MWwhen integrated with coal gasification, coal slurry feed, drying andfuel gas treatment system having the follwoing characteristics.

    ______________________________________                                        Air flow to air separation                                                                 9.12 Kg/sec                                                      unit                                                                          Oxygen produced                                                                            2.09 Kg/sec                                                      Oxygen purity                                                                              93%                                                              Oxygen pressure                                                                            1800 kPa absolute                                                Coal gasifier                                                                              Otto Saarberg type high temperature slagging                                  unit                                                             Operating pressure                                                                         1100 kPa absolute                                                Operating temperature                                                                      1,500° C.                                                 Coal feed    Bituminous coal as 30% coal wt/wt coal/water                                  slurry                                                           Coal analysis (dry)                                                           Volatile matter                                                                            41.5%                                                            Ash          6.0%                                                             c.v. (dry and ash free)                                                                    32.2 MJ/kg                                                       Ash fusion flow                                                                            1,450° C.                                                 temperature                                                                   Coal feed rate                                                                             2.11 Kg/sec (dry and ash free)                                   Coal slurry pressure                                                                       3,000 kPa absolute                                               Coal slurry temperature                                                                    Heated to 220° C. by heat exchange with the                            turbine exhaust prior to injection into the                                   integrated dryer                                                 Gas analysis (dry)                                                            H2           32.3% (volume)                                                   CO           58.8%                                                            CO2          3.3%                                                             N2           5.2%                                                             H2S + COS    0.4%                                                             Exit drying and gasifi-                                                       cation stages                                                                 Gas (dry)    4.80 Kg/sec                                                      Water vapour 5.40 Kg/sec                                                      Exit final adiabatic                                                          cooling and gas                                                               purification stage                                                            Gas (dry)    4.80 Kg/sec                                                      Water vapour 7.39 Kg/sec                                                      Fuel gas recuperator                                                                       90%                                                              effectiveness                                                                 ______________________________________                                    

The pre-heated fuel gas and air are mixed in parallel venturi mixersimmediately beneath the lower tube sheet of two combustors eachcontaining 3,000 2 meter long 25 mm outside diameter silicon carbidetubes arranged generally in accordance with co-pending patent PCTAU95/07719. In this case no secondary combustion stage is used.

    ______________________________________                                                         27.2 MW                                                      ______________________________________                                        Net efficiency     40%                                                        exit NOX           less than 10 p.p.m.                                        ______________________________________                                    

While various embodiments of the present invention have been describedin detail, it is apparent that modifications and adaptations of thoseembodiments will occur to those skilled in the art. However, it is to beexpressly understood that such modifications and adaptations are withinthe scope of the present invention, as set forth in the followingclaims.

What is claimed is:
 1. A process for the gasification of carbonaceousfuels for the production of energy, comprising:(i) introducing anaqueous slurry of coal and hot gas into a drying stage, wherein saidaqueous slurry of coal has at least 55% by weight of water, and whereinsaid hot gas is produced in a hot-gas producing coal gasifier; (ii)drying said aqueous slurry of coal in said drying stage by the adiabaticcooling of said hot gas and evaporation of the water to produce a driedcoal and a cooled humidified gas; (iii) separating said dried coal andsaid cooled humidified gas; (iv) adding said dried coal to said hot-gasproducing coal gasifier; (v) further cooling and cleaning said cooledhumidified gas to produce a cleaned gas; and (vi) introducing saidcleaned gas to a recuperated turbine and combustor arrangement, whereinsaid recuperated turbine comprises a compressor unit, an expansion unitand a generator, and wherein said cleaned gas is heated, combined withheated pressurized air from the compressor, combusted in a combustor andtransferred to the expansion unit for subsequent power generation. 2.The process of claim 1, wherein said aqueous slurry comprises a slurrycomprising coal washery tailings residue.
 3. The process of claim 1,wherein said aqueous slurry comprises waste water and sewerage.
 4. Theprocess of claim 1, wherein said aqueous slurry is in the form of apumpable paste.
 5. The process of claim 1, wherein said combustor is atwo stage combustor, and wherein at least most of said cleaned gas isheated and combined with compressed air in the first stage of said twostage combustor and transferred to the second stage of said two stagecombustor, and wherein said compressed air is generated by saidcompressor unit.
 6. The process of claim 5, wherein at least a portionof said cleaned gas directly enters the second stage of the of said twostage combustor via a catalytic system and is admixed with the gas fromthe first stage of said two stage combustor.
 7. The process of claim 6,wherein combustion in the second stage of said two stage combustor ispredominantly free radical combustion.
 8. The process of claim 5,wherein said hot gas subsequently mixed and combusted in the secondstage of said two stage combustor is first reacted over a shift catalystto maximize the hydrogen content in that part of the hot gas.
 9. Theprocess of claim 1, wherein at least a portion of said hot gas producedby said coal gasifier and a subsequent gas purification system is mixedwith the preheated air to form a fuel and air mixture below its lowerexplosive limit and the mixture is then combusted.
 10. The process ofclaim 9, wherein at least a portion of said hot gas is added to andcombusted in combustion gases leaving said combustor by mixing theadditional hot gas with the hot combustion gases leaving said combustorunder highly turbulent conditions so as to minimize flame reactions andmaximize free radical induced combustion of the added hot gas.
 11. Theprocess of claim 10, wherein the turbine has a compression ratio below35/1.
 12. The process of claim 1, wherein air used for gasification insaid coal gasifier is preheated by recuperation with exhaust gasesleaving said recuperated turbine whereby an air-blown gasifier isoperated at a high temperature to enable slagging of the ash and saltscontained in the aqueous slurry.
 13. An apparatus for the burning ofcarbonaceous fuel for the production of energy comprising:a gasifierinto which an aqueous coal slurry comprising at least 55% by weight ofwater is introduced; a flow drier/separator, wherein materials exitingthe gasifier are dried and separated into a gaseous component and adried slurry material, and wherein the dried slurry material is fed backto the gasifier; a cooling/cleaning device, wherein the gaseouscomponent from said drier/separator is cooled and cleaned to produce acooled and cleaned gas; and a recuperator turbine/combustion device forgenerating energy using the cooled and cleaned gas.
 14. An apparatus forthe burning of carbonaceous fuel for the production of electrical energycomprising:a gasifier into which an aqueous coal slurry comprising atleast 55% by weight of water is introduced; a flow drier/separator,wherein materials exiting the gasifier are dried and separated into agaseous component and a dried slurry material, and wherein the driedslurry material is fed back to the gasifier; a cooling/cleaning device,wherein the gaseous component from said drier/separator is cooled andcleaned to produce a cooled and cleaned gas; and a gas turbinegeneration unit comprising a compressor, an expansion stage, a gasturbine generator, and a combustor mechanism, the arrangement being suchthat combustion and process air passes from said compressor in a firststream to the gasifier and in a second stream to the combustor, wherethe second stream is combined with the cooled and cleaned gas, thecombined gasses then being passed to said expansion stage of said gasturbine generator, and converted therein into electrical energy.